This invention is directed to a process for producing twisted steel wire cord in a manner which completely departs from the conventional practice. More particularly, the process involves forming a twisted precursor cord by textile methods and then converting the precursor to steel cord.
Composites of steel and rubber, wherein reinforcing elements of corded steel are bonded to rubber, find wide application in a variety of products which include, for example, conveyor belts, heavy duty hoses, pulley belts and pneumatic tires. The application of such composites in the fabrication of pneumatic tires has become particularly important. That is, there has been an ever increasing use of steel cord to provide the need for a more effective reinforcement of both the belt and carcass in modern vehicular tires.
In the conventional practice, steel tire cord and steel cord for other applications is made by cabling drawn steel wire about a central axis to provide a strand or cord having the desired twist level. This cabling operation generally results in a substantial retention of bending stresses which causes the cord to kink or curl in a helical, spring-like configuration. To reduce the retained stresses, the cord is customarily "killed" either by back twisting, stress relieving, or by mechanical means. However, such treatments are not done without sacrifice of desirable properties. In the case of stress relieving, the cord is heated to relieve the retained stress which causes losses in the tensile property. Mechanical killing, on the other hand, involves plastic deformation of the live strand or cord by sequentially bending the strand or cord over a series or rolls. This treatment typically causes scoring of the steel cord and losses in desirable properties.
Besides the afore-mentioned difficulties, the cost of steel wire produced by the traditional wire drawing procedures is relatively expensive. This becomes apparent when one considers the steps involved merely to obtain the intermediate steel wire rod product. That is, molten steel is cast into ingots which are subsequently rolled into blooms from which billets are formed. Finally, the billet is hot rolled to produce the steel wire rod. The wire rod must then undergo a series of elaborate and costly metal-drawing operations to obtain a steel wire product suitable for use as tire cord or in other applications wherein a relatively fine diameter is required.
It is, therefore, an object of this invention to provide an entirely new and more convenient approach to the production of steel wire cord.
It is a further object of the invention to provide a method for producing corded steel wire which is substantially less costly than the conventional practice.